Dependent products of monoids

Content created by Egbert Rijke and Fredrik Bakke.

Created on 2023-03-13.
Last modified on 2023-03-19.

module group-theory.dependent-products-monoids where
open import foundation.dependent-pair-types
open import foundation.function-extensionality
open import foundation.identity-types
open import foundation.sets
open import foundation.universe-levels

open import group-theory.dependent-products-semigroups
open import group-theory.monoids
open import group-theory.semigroups


Given a family of monoids Mᵢ indexed by i : I, the dependent product Π(i : I), Mᵢ is a monoid consisting of dependent functions taking i : I to an element of the underlying type of Mᵢ. The multiplicative operation and the unit are given pointwise.


module _
  {l1 l2 : Level} (I : UU l1) (M : I  Monoid l2)

  semigroup-Π-Monoid : Semigroup (l1  l2)
  semigroup-Π-Monoid = Π-Semigroup I  i  semigroup-Monoid (M i))

  set-Π-Monoid : Set (l1  l2)
  set-Π-Monoid = set-Semigroup semigroup-Π-Monoid

  type-Π-Monoid : UU (l1  l2)
  type-Π-Monoid = type-Semigroup semigroup-Π-Monoid

  mul-Π-Monoid : (f g : type-Π-Monoid)  type-Π-Monoid
  mul-Π-Monoid = mul-Semigroup semigroup-Π-Monoid

  associative-mul-Π-Monoid :
    (f g h : type-Π-Monoid) 
    mul-Π-Monoid (mul-Π-Monoid f g) h 
    mul-Π-Monoid f (mul-Π-Monoid g h)
  associative-mul-Π-Monoid =
    associative-mul-Semigroup semigroup-Π-Monoid

  unit-Π-Monoid : type-Π-Monoid
  unit-Π-Monoid i = unit-Monoid (M i)

  left-unit-law-mul-Π-Monoid :
    (f : type-Π-Monoid)  mul-Π-Monoid unit-Π-Monoid f  f
  left-unit-law-mul-Π-Monoid f =
    eq-htpy  i  left-unit-law-mul-Monoid (M i) (f i))

  right-unit-law-mul-Π-Monoid :
    (f : type-Π-Monoid)  mul-Π-Monoid f unit-Π-Monoid  f
  right-unit-law-mul-Π-Monoid f =
    eq-htpy  i  right-unit-law-mul-Monoid (M i) (f i))

  is-unital-Π-Monoid : is-unital-Semigroup semigroup-Π-Monoid
  pr1 is-unital-Π-Monoid = unit-Π-Monoid
  pr1 (pr2 is-unital-Π-Monoid) = left-unit-law-mul-Π-Monoid
  pr2 (pr2 is-unital-Π-Monoid) = right-unit-law-mul-Π-Monoid

  Π-Monoid : Monoid (l1  l2)
  pr1 Π-Monoid = semigroup-Π-Monoid
  pr2 Π-Monoid = is-unital-Π-Monoid

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